IPv4 address length technical design

William Herrin bill at herrin.us
Wed Oct 3 20:13:17 UTC 2012


On Wed, Oct 3, 2012 at 3:22 PM, Izaac <izaac at setec.org> wrote:
> On Wed, Oct 03, 2012 at 06:52:57PM +0200, Seth Mos wrote:
>> "Pick a number between this and that." It's the 80's and you can
>> still count the computers in the world. :)
>
> And yet, almost concurrently, IEEE 802 went with forty-eight bits.  Go
> figure.  I'm pretty sure the explanation you're looking for is: It was
> with the word size of the most popular minis and micros at the time.

It wasn't. At the time. But at some point people of vision figured out
that CPU word sizes would standardize on power-of-two powers of two.
Really helps when you want to align data elements in memory if exactly
2 16 bit integers fit in the 32 bit word and exactly 2 32 bit integers
fit in the 64 bit word. "And a half" is a phrase that makes life
miserable in both software development and hardware design.

IEEE figured it out later. The replacement for the MAC address is
EUI-64. I still haven't figured out Bell's excuse with ATM.

Regards,
Bill Herrin

-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
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